A linear actuator disclosed in FIG. 1 of Japanese Patent Application Publication No. 2009-118732 (JP2009-118732β) includes a hollow rotary shaft 303 that is rotatable along with rotational motion of a motor, a ball screw nut 315 fixed to a first end 303A of the rotary shaft 303 in the longitudinal direction, and a ball screw 317 threadably engaged with the ball screw nut 315. As the ball screw nut 315 rotates along with rotational motion of the rotary shaft 303, the ball screw 317 makes linear motion in the axial direction of the rotary shaft 303. In the linear actuator, a second end 303B of the rotary shaft 303 in the axial direction is closed, and a disc 347 of an electromagnetic brake device 345 is provided at the second end 303B of the rotary shaft 303 (see FIG. 9).
In the linear actuator according mentioned above, however, the disc 347 of the electromagnetic brake device 345 is attached to the closed second end 303B of the rotary shaft 303, and therefore the ball screw 317 cannot move through the inside of the electromagnetic brake device 345. That is, the ball screw 317 can move no further than the second end 303B of the rotary shaft 303, at which the electromagnetic brake device 345 is provided. Therefore, in this linear actuator, the moving distance of the ball screw 317 serving as an output shaft is restricted (see FIG. 9).